Electromagnetic actuator

ABSTRACT

An electromagnetic actuator according to the present invention comprises 
     (a) a casing mainly consisting of a stationary iron core (1) or a combination of a stationary iron core (1) and a yoke, (1b), the casing being formed with at least one of opening; 
     (b) one or a pair of movable iron core (2) as an actuating member, capable of reciprocally moving through the opening of the casing; 
     (c) an electric winding element (4) arranged in the casing for applying a first magnetomotive force to the movable iron core (2) when an electric current is flowed through the winding element (4); 
     (d) a permanent magnet (5) being so arranged in the casing as to apply the second magnetomotive force to the movable iron core; and 
     (e) a bias force generating means (3) for applying a mechanical force or the first magnetomotive force to the movable iron core (2), wherein the improvement is characterized that a permanent magnet (5) is so arranged in the casing as to apply the second magnetomotive force in parallel to the first magnetomotive force to the movable iron core. 
     The electromagnetic actuator can be operated by a fine current, generate large thrust and be used in a electromagnetic valve, or the like.

Technical Field

The present invention generally relates to an electromagnetic actuatorwhich electrically controlls mechanical force for electromagneticdevices such as electro-magnetic relay, electromagnetic switch,electromagnetic valve, electromagnetic locking means, electromagneticbrake, electromagnetic clutch, electromagnetic vibrator, or the like.

PRIOR ARTS

In various field of industrial art, public use and so on, conventionallyused electromagnetic actuators are generally composed of a combinationof electromagnetic attraction of an electromagnet and spring bias force.For a specific use, it is well known that an electromagnetic actuatorwith self-supporting ability (latching property) is composed of anelectromagnet, a spring, and a permanent magnet as a self-latchingmeans.

Referring to FIGS. 9(a),(b), there is shown a constitution of mostcommonly used plunger type electromagnetic actuator in the prior art.That is, in the drawing, this plunger type electromagnetic actuatorcomprises a stationary element consisting of a stationary iron core 1and a winding element 4 wound round the core 1, a plunger shape movableiron core 2 capable of reciprocating with respect to the iron core 1,and a spring 3 generating a bias force so as to maintain a gap 1abetween the stationary iron core 1 and the movable iron core 2 while thewinding element 4 is free from an electric current.

FIG. 9(a) shows this OFF-state of this plunger type electromagneticactuator; that is, the plunger shape movable iron core 2 is present tothe iron core 1 under mechanical stable condition on account of thefunction of the spring 3 which applys the bias force in the directionshown by an arrow 3a to the movable core 2.

When an electric current is flowed through the winding element 4 asshown in FIG. 9(b), a magnetic flux 27 is generated so that a magneticattractive force will be also caused in the reverse direction of thebias force 3a and the magnetic attractive force is greater than the biasforce. Accordingly, the plunger shape movable iron core 2 is forcedlymoved towards the stationary iron core 1 and contacted thereto as shownin FIG. 9(b). In this way, an actuating member connected to the movableiron core 2 such as an electric contact piece, a valve rod or like ( notshown ) can be mechanically actuated.

This mechanical actuated state is maintained during the ON-state of thewinding element 4. On the other hand, the movable iron core 2 will bereturned to the mechanical stable state as shown FIG. 9(a) due to thebias force of the spring 3 if the winding element 4 is switched from theON-state to the OFF-state.

Referring to FIGS. 10(a)(b), there is shown another conventionalelectromagnetic actuator which is additionally provided with a permanentmagnet for latching. That is, this latching type electromagneticactuator is so constituted that the magnetomotive force of the permanentmagnet 5 is applied in series to the magnetomotive force of the magneticcircuit consisting of the stationary iron core 1, the movable iron core2 and the gap 1a as shown in FIGS. 9(a),(b).

When the winding element 4 is present in the OFF-state; i.e., anelectric current is not flowed therethrough, the magnetic flux 26 causedby the magnetic force of the permanent magnet 5 applys the attractiveforce to the movable iron core 2 which is always subjected to the biasforce in the direction of arrow 3a by means of the spring 3. Since thisattractive force by the permanent magnet 5 exists in equilibrium withthe bias force of the spring 3, the movabble iron core 2 is isolatedfrom the stationary iron core 1 with a gap 1a therebetween. This stateis referred as "first mechanical stable state".

Nextly, when an electric current in a series of pulses is flowed throughthe winding element 4 in the direction as shown in FIG. 10(a), themagnetic flux 27 is generated and overlapped with the magnetic flux 26caused by the permanent magnet 5 so that the magnetic attractive forcegreater than the bias force ( arrow 3a ) of the spring 3 is generated.Thus the movable iron core 2 is attracted and forcedly moved towards thestationary iron core 1. As a result, the movable iron core 2 contacts tothe stationary iron core 1. This state is shown in FIG. 10(b) andreferred as "second mechanical stable state". In this way, an actuatingmember connected to the movable iron core 2 such as an electric contactpiece, valve rod or the like (not shown ) can be mechanically actuated.

Under this second mechanical stable state, an electric current in aseries of pulses is flowed in the direction shown in FIG. 10(b) so thatthe magnetic flux 27 in the counter direction to the magnetic flux 26caused by the permanent magnet 5 will be generated. Thus the movableiron core 2 is free from the magnetic attractive force so that themovable iron core 2 will return to the first mechanical stable state bythe bias force ( arrow 3a) shown in FIG. 10(a) and will be maintained inthis state.

The former mentioned conventional plunger type electromagnetic actuatorshown in FIGS. 9(a),(b)however has the following problems.

(a) Ampere turns required for the desired attractive force and desiredstroke of actuator becomes greater.

(b) Since it is required to maintain the actuator in ON-state when theactuator is kept in its actuating position, this actuator consumesgreater electric energy.

(c) As the electric energy is consumed, the winding element generatesheat. In order to control a rise in temperature in the winding element,the size of the electromagnetic actuator will be increased.

Although the latter mentioned conventional electromagnetic actuatorhaving the latching property shown in FIGS. 10(a),(b) has a merit thatboth mechanical stable states can be easily switched to the other byapplying the electric current in a series of pulses in an instant andthus this actuator can be controlled by a small amount of electricenergy.

However, since the permanent magnet 5 having a great reluctance isarranged in the magnetic circuit in series which is energized by thewinding element 4, this actuator requires the ampere turns forenergizing several times as large as the former actuator shown in FIGS.9(a),(b). So this actuator requires a great capacity of power source forenergizing this electromagnetic element and / or to increase the size ofwinding element. Further, this actuator causes a problem that therequired values of ampere turns for switching on and off are remarkabledifferent from each other.

DESCRIPTION OF THE INVENTION

With these problems in mind, it is the primary object of the presentinvention to provide an improved electromagnetic actuator which is ahighly sensitive and saves electric power type actuator capable ofcontrolling with a power source of fine capacity.

Further, it is another object of the present invention to provide acompact, simple and strongly built electromagnetic actuator.

To accomplish the above objects, the electromagnetic actuator accordingto the present invention can be performed in accordance with thefollowing knowledge.

Referring to FIG. 5 and FIG. 6, they are schematic illustrations showingthe operation principles of the actuator according to the presentinvention and the conventional actuator, respectively. In thesedrawings, the same numbers designate the same or corresponding elementsalready mentioned in FIG. 9 and FIG. 10.

First of all, in FIG. 5 the magnetic flux generated by the permanentmagnet 5 is flowingly divided into the leftside and rightside flux flowsφb and φa at a pole piece 16. The magnetic flux φi is generated as anelectric current is flowed through the winding element 4.

In the conventional plunger type electromagnetic actuator shown in FIG.6, the magnetic flux φio is also generated as an electric current isflowing through the winding element 4.

If the bias force of the spring 3 in the direction shown by the arrow 3ais represented by Fs, the value of proporional constant K is assumed tobe equivalent for both actuators, and leaking magnetic flux is ignored,then the attractive force Fa, Fb of the actuators according to thepresent invention and the conventional electromagnetic actuator will berepresented by the following equations.

    Fa=K(φa+φi).sup.z -FS                              . . . (1)

    Fb=K(φio).sup.2 -FS                                    . . . (2)

Further, Fs is eliminated in order to simplify the equations and thenthe following equations are assumed.

    φa=α·φi                             . . . (3)

    φi=φio                                             . . . (4)

These conditions are substituted into the equations (1) and (2) and theyare rearranged in order to obtain the ratio of Fa and Fb, therebyresulting in the following equation.

    Fa/Fb≈(φa+φi).sup.z /(φio).sup.z =(α+1).sup.z . . . ( 5)

According to this equation, as is clear from the curve shown in FIG. 7,the actuator accroding to the present invention can easily generate theattractive force several times as great as that of the prior art underthe same condition; i.e., the same value of the ampere turns forenergizing, in accordance with the value of α.

Nextly, according to the equations (1),(2) and (3), assuming that thevalue of Fa is equivalent to that of Fb;

    Fa=Fb                                                      . . . (6)

then the following equation will be obtained.

    φi/io=1/(α+1)                                    . . . (7)

According to equation (7), as is clear from the curve shown in FIG. 8 inaccordance with the value of α, the actuator of the present inventioncan easily generate the same value of the attractive force as that ofthe prior art at the small value of ampere turns in comparison with theprior art.

Although the above assumption has been obtained after no-considerationof the influence of increase of magnetic reluctance caused by thedivided magnetic flow material 17 against the magnetic flux φi, theinfluence can be so minimized as to be neglected in practical manner.

The first and second present inventions have been achieved in accordancewith the above assumed knowledge. That is, the electromagnetic actuatoraccording to the first present invention comprises:

A permanent magnet (5); a pole piece (16) having a first pole facesecured to a first pole face of the permanent magnet (5); a pair ofmovable iron cores (2) so arranged that the inner end faces (2a) of thetwo cores (2) can be moved close to or apart from a pair of second polefaces (16a) of the pole pieces (16) and are connected through anon-magnetic connecting shaft (8); a stationary iron core (1) havingfirst pole faces (1f) facing respectively a side surface (2b) meeting atright angles with the inner end face (2a) each of the movable iron cores(2) through a fine gap (1n) and a second pole face (1f) secured to asecond pole face of the permanent magnetic (5); a pair of dividingmagnetic paths (17) having a required magnetic reluctance and eachdividing magnetic path (17) being fixed to an outer end face (2h) ofeach of the movable iron cores (2) and a winding element (4) forenergizing the magnetic circuit consisting of the stationary iron core(1), the movable iron cores (2), the pole pieces (16), and the dividingmagnetic paths (17).

And the electromagnetic actuator according to the second presentinvention comprises; a permanent magnet (5); a pole piece (16) having afirst pole face secured to a first pole face of the permanent magnet (5)and a second pole face at the inner surface of a recessed or penetratedspace (16d); a movable iron core (2) so arranged that an end (2i) of themovable iron core (2) can be moved into or out of the recessed orpenetrated space (16d); a stationary iron core (1) having a first poleface (1f) facing a side surface (2b) of the movable iron core (2)through a fine gap (1n) and a second pole face (11) secured to a secondpole face of the permanent magnet (5); a pair of dividing magnetic paths(17) having a required magnetic reluctance interposed between a thirdpole face (16b) of the pole piece (16) and a third pole face (1k) of thestationary iron core (1); a winding element (4) for energizing amagnetic circuit consisting of the stationary iron core (1), the movableiron core (2), the pole piece (16), and the dividing magnetic paths(17); and a spring (3) interposed between the movable iron core (2) andthe pole piece (16) or the stationary iron core (1) in order to applymechanical bias force to the movable iron core (2).

As given explanation above, the electromagnetic actuator according tothe first and second present inventions can provide the followingexcellent effects in comparison with the conventional device.

(1) The present invention can generate the magnetic attractive forceremarkably greater than that of the conventional device by using thesame winding element for generating the equivalent magnetomotive force.

(2) The present invention can generate the magnetic attractive forceequivalent to the conventional device by using the winding element forgenerating the magnetomotive force remarkably smaller than theconventional device.

(3) The present invention can provide the alternative functions of asingle stable state operation and a two-stable states operation by thesame composition.

(4) The above effects provide further detailed features;

(a) The capacity of power source for operating this device is relativelysmall;

(b) The highly sensitive and energy saving type device can be achieved;

(c) The compact sized and light weight device can be achieved;

(d) Simple structure with water proof, pressure resistive, and dustproof properties can be easily achieved.

BRIEF DESCRIPTON OF THE DRAWINGS

FIG. 1 is a schematic illustration showing a embodiment of anelectromagnetic actuator according to the first present invention;

FIG. 2(a) is a schematic illustration showing a embodiment of anelectromagnetic actuator according to the second present invention whichis present in its first mechanical stable state;

FIG. 4(b) is a schematic illustration showing the second mechanicalstable state of the actuator shown in FIG. 4(a);

FIG. 3 is a schematic illustration showing a principle of theelectromagnetic actuator according to the first and second presentinventions;

FIG. 6 is a schematic illustration showing a principle of a conventionalelectromagnetic actuator;

FIG. 5 and FIG. 6 are graphs showing characteristics curves of theelectromagnetic actuator according to the present invention shown inFIG. 5;

FIG. 9(a) is a schematic illustration showing a conventionalelectromagnetic actuator in its first mechanical stable state;

FIG. 9(b) is a schematic illustration showing the second mechanicalstable state of the conventional actuator shown in FIG. 9(a);

FIG. 10(a) is a schematic illustration showing another conventionalelectromagnetic actuator in its first mechanical stable state; and

FIG. 10(b) is a schematic illustration showing the second mechanicalstable state of the actuator shown in FIG. 10(a).

PREFERRED EMBODIMENTS FOR EMBODYING THE FIRST AND SECOND PRESENTINVENTIONS

Referring to FIG. 3, there is shown an embodiment of an electromagneticactuator according to the first present invention comprising a permanentmagnet 5; a pole piece 16 having a first pole face secured to a firstpole face of the permanent magnet 5; a pair of movable iron cores 2 soarranged that the inner end faces 2a of both cores 2 can be moved closeto or apart from a pair of second pole faces 16a of the pole pieces 16and are connected through a non-magnetic connecting shaft 8; astationary iron core 1 having first pole faces 1f facing respectively aside surface 2b meeting at a right angle with the inner end face 2a ofeach movable iron cores 2 through a fine gap 1n and a second pole face1l secured to a second pole face of the permanent magnet 5; a pair ofdividing magnetic paths 17 having a required magnetic reluctance andeach dividing magnetic path 17 being fixed to an outer end face 2h ofeach of the movable iron cores 2; and a winding element 4 for energizingthe magnetic circuit consisting of the stationary iron core 1, themovable iron cores 2, the pole pieces 16, and the dividing magneticpaths 17.

An operation on such constituted embodiment of the electromagneticactuator will be explained.

FIG. 3 shows a first mechanical stable state.

Under this condition, when an electric current in a series of pulses isflowed through the winding element 4 in the flowing direction as shownin FIG. 3, the magnetic flux φ i is overlaps the magnetic flux φ b.Thus, the moveable iron core 2 is subjected to the magnetic attractiveforce so that the movable iron core 2 will be moved toward the rightside and maintained in the state; i.e., the second mechanical stablestate.

In this second mechanical stable state, when the electric current in aseries of pulses is flowed through the winding element 4 in the reversedirection as shown in FIG. 3, the reverse magnetic flux of the magneticflux φ i is generated so that the movable iron core 2 is finallypositioned in the first mechanically stable state shown in FIG. 3.

That is, a pair of movable iron cages 2 is connected through anon-magnetic connecting rod 8 and is so arranged that an inner end face2a of each of the movable iron cores 2 can be moved close to or apartfrom a second pole face 16a of a pole piece 16. Further, a stationaryiron core 1 has a pair of first pole faces 1f facing to the side surface2b meeting at a right angle with the inner end face 2a of the movableiron core 2 through a fine gap 1n and a second pole face 11 secured to asecond pole face of a permanent magnet 5. A pair of dividing magneticpaths 17 having required magnetic reluctance is fixed to the outer endfaces 2h of the movable iron cores 2.

According to this constituted actuator, any one of the movable ironcores 2 and the dividing magnetic paths 17 can be operated alternativelyas an electric current is flowed through the winding element 4. As aresult, there is no means for generating mechanical bias force such as aspring.

Next, referring to FIGS. 4(a) and 4(b), there is shown an embodiment ofthe electromagnetic actuator according to the second present inventioncomprising a permanent magnet 5; a pole piece 16 having a first poleface secured to a first pole face of the permanent magnet 5 and a secondpole face at the inner surface of a recessed or penetrated space 16d; amovable iron core 2 so arranged that an end 2i of the movable iron core2 can be moved into or out of the recessed or penetrated space 16d; astationary iron core 1 having a first pole face 1f facing to a sidesurface 2b of the movable iron core 2 through a fine gap 1n and a secondpole face 1l secured to a second pole face of the permanent magnet 5; adividing magnetic path 17 having a required magnetic reluctanceinterposed between a third pole face 16b of the pole piece 16 and athird pole face 1k of the stationary iron core 1; a winding element 4for energizing a magnetic circuit consisting of the stationary iron core1, the movable iron core 2, the pole piece 16, and the dividing magneticpath 17; and a spring 3 interposed between the movable iron core 2 andthe pole piece 16 or the stationary iron core 1 in order to applymechanical bias force to the movable iron core 2.

An operation of this embodiment will be discussed as follows:

FIG. 4(a) shows a first mechanical stable state where an electriccurrent is not flowed through the winding element 4. That is, the biasforce 3a caused by the spring 3 exists in equilibrium with theattractive force of the magnetic flux φ a and φ b owing to themagnetomotive force of the permanent magnet 5 so that the movable ironcore 2 is maintained at the position where a required space is definedbetween the end 2i of the movable iron core 2 and the recess 16d of thepole piece 16.

Under this condition, when an electric current in a series of pulses isflowed through the winding element 4 in the flowing direction as shownin FIG. 4(a), the magnetic flux φ i in the directio represented by thearrow represented in solid line is generated, and cancelled against themagnetic flux φ a and overlapped with the magnetic flux φ b. Thus, themovable iron core 2 is subjected to the magnetic attractive forcegreater than the bias force 3a of the spring 3. Then the movable ironcore 2 contacts the pole piece 16 and is maintained in this state asshown in FIG. 4(b). This state is a second mechanical stable state.

In this second mechanical stable state, when the electric current in aseries of pulses is flowed through the winding element 4 in thedirection as shown in FIG. 4(b), the magnetic flux φ i2, in thedirection shown in FIG. 4(b); i.e., the reverse direction of magneticflux φ i in FIG. 4(a); is generated. Thus, this magnetic flux φ i2 iscancelled against the magnetic flux φ b and overlapped with the magneticflux φ a so that the magnetic attractive force is decreased. The movableiron core 2 is separated from the pole piece 16 owing to the bias forceof the spring 3 and finally positioned in the first mechanical stablestate shown in FIG. 4(a).

A pole piece 16 is formed with a recess 16d as shown in the drawing. Amovable iron core 2 is so arranged that an end 2i of the movable ironcore 2 can be inserted in or drawn from the recess 16d. The recess 16din the pole piece 16 may be formed as a penetrated hole.

An operation on the embodiment is designed that the maximum attractiveforce exhibits at the initial state of attracting motion and it ispossible to provide a device with compact, light and low impact noisegenerated when the movable iron core 2 is contacted with the pole piece16.

UTILIZING FIELD IN INDUSTRIAL FIELD

The devices according to the present first and second invention can beutilized for various commonly used devices such as electromagneticrelay, electromagnetic valve, electric locking device, electromagneticsieve, and so on which are compact, high sensitive, light and low-energyconsumed devices capable of working by a tiny power source such as asolar battery, a dry cell or the like.

I claim:
 1. An electromagnetic actuator comprising;a permanent magnet(5); a pole piece (16) having a first pole face secured to a first poleface of the permanent magnet (5); a pair of movable iron cores (2) soarranged that the inner end faces (2a) of the both cores (2) can bemoved close to or apart from a pair of second pole faces (16a) of thepole pieces (16) and are connected through a non-magnetic connectingshaft (8); a stationary iron core (1) having first pole faces (1f)facing respectively a side surface (2b), meeting at a right angle withthe inner end face (2a), of each of the movable iron core (2) through afine gap (1n) and a second pole face(1l) secured to a second pole faceof the permanent magnet (5); a pair of dividing magnetic paths (17)having a required magnetic reluctance and each dividing magnetic path(17) being fixed to an outer end face (2h) of each the movable iron core(2); and a winding element (4) for energizing the magnetic circuitconsisting the stationary iron core (1), the movable iron cores (2), thepole pieces (16), and the dividing magnetic paths(17).
 2. Anelectromagnetic actuator comprising;a permanent magnet (5); a pole piece(16) having a first pole face secured to a first pole face of thepermanent magnet (5) and a second pole face at the inner surface of arecessed or penetrated space (16d) ; a movable iron core (2) so arrangedthat a end (2i) of the movable iron core (2) can be moved into or out ofthe recessed or penetrated space (16d); a stationary iron core (1)having a first pole face (2f) facing to a side surface (2b) of themovable iron core (2) through a fine gap (1n) and a second pole face(1l) secured to a second pole face of the permanent magnet (5); adividing magnetic path (17) having a required magnetic reluctanceinterposed between a third pole face (16b) of the pole piece (16) and athird pole face (1k) of the stationary iron core (1); a winding element(4) for energizing a magnetic circuit consisting of the stationary ironcore (1), the movable iron core (2), the pole piece (16), and thedividing magnetic path (17); and a spring (3) interposed between themovable iron core (2) and the pole piece (16) or the stationary ironcore (1) in order to apply mechanical bias force to the movable ironcore (2).